1- If you work had not been done, then you don’t have to fulfill the vow. A vow must be fulfilled when the condition is met (meaning you get the work done).
2- Did you make a religious vow? Meaning you said “it is upon me for Allah to pray this namaz if I get my work done,” or you simply made a promise? If you made a promise, even though it’s not good to break it, but it’s not haram and you don’t have to pay a kaffara. But if you made a religious vow (nazr) and your work gets done, then you must pray the namaz everyday. If you don’t then you have to pay kaffara (feeding 10 poor people).
2- I recommend these Du’as:
One: https://www.duas.org/Amn.htm
Two:
اللَّهُمَّ رَبَّ السَّمَاوَاتِ السَّبْعِ وَ مَا بَيْنَهُنَّ وَ رَبَّ الْعَرْشِ الْعَظِيمِ، وَ رَبَّ جَبْرَئِيلَ وَ مِيكَائِيلَ وَ إِسْرَافِيلَ، وَ رَبَّ الْقُرْآنِ الْعَظِيمِ، وَ رَبَّ مُحَمَّدٍ خَاتَمِ النَّبِيِّينَ ، إِنِّي أَسْأَلُكَ بِالَّذِي تَقُومُ بِهِ السَّمَاءَ، وَ بِهِ تَقُومُ الْأَرْضَ، وَ بِهِ تُفَرِّقُ بَيْنَ الْجَمْعِ، وَ بِهِ تَجْمَعُ بَيْنَ الْمُتَفَرِّقِ، وَ بِهِ تَرْزُقُ الْأَحْيَاءَ، وَ بِهِ أَحْصَيْتَ عَدَدَ الرِّمَالِ وَ وَزْنَ الْجِبَالِ وَ كَيْلَ الْبُحُورِ
Then say Salawat and ask for you Hajat.
Three: Recite Ziyarat Ashura for 40 days